/prime-multiplier

Primary LanguageClojure

prime-multiplier

It's a solution to a code challenge, requiring a program:

  • that prints out a multiplication table of the first 10 prime numbers
  • that must run from the command line and print one table to STDOUT
  • where the first row and column of the table should have the 10 primes, with each cell containing the product of the primes for the corresponding row and column

Considerations:

  • Complexity: How fast does your code run? How does it scale?
  • Consider cases where we want N primes.
  • Do not use the Prime class from stdlib (write your own code).
  • Write tests. Try to demonstrate TDD/BDD

Implementation

Clojure

This is primarily written in Clojure.

It uses Leiningen for project automation. Go there for installation instructions.

Tests are written using Speclj.

Running

With Leiningen

Install Leiningen using the instructions in the link above.

Before running the app using Leiningen, run the following command froFixes typoFixm the project root:

lein deps

This will cause Leiningen to update all the dependencies listed in the project.clj file.

Using lein run

Running without options produces a table of the products of the first ten prime numbers: $ lein run

Running with an argument allows you to choose the number of primes to be multiplied: $ lein run <n-primes>

For example:

$ lein run 10 works fine

$ lein run "10" works fine too.

n-primes can be quoted "10" or unquoted 10 and will be parsed if necessary.

Using lein uberjar

You can create a runnable jar using:

$ lein uberjar

You can then run it like any other Java app:

$ java -jar prime-multiplier-0.1.0-SNAPSHOT-standalone.jar

$ java -jar prime-multiplier-0.1.0-SNAPSHOT-standalone.jar <n-primes>

Running Tests (Specs)

With Leiningen

Speclj includes a Leiningen task.

$ lein spec

Using lein run

Speclj also includes a Clojure main namespace:

$ lein run -m speclj.main

As a Java command

And sometimes it's just easier to run a Java command, like from an IDE.

$ java -cp <...> speclj.main

$ java -cp `lein classpath` speclj.main

tl;dr

Things to do:

  • Improve command line arguments using clojure.tools/cli

  • Give it a nice command besides lein or java -jar, something like prime-table

  • Package as a Docker app

  • Look into performance upgrades:

    • Use a better prime-generation algorithm that doesn't blow the stack
    • Only calculate the products needed once. Iterating over every row and column intersect is wasteful.